The present application relates to laser devices, specifically to fiber coupled laser devices having high polarization extinction ratio and low noise.
Polarization maintaining (PM) fiber coupled lasers, for their strong polarization maintaining capacities, play a more and more important role in optical communication, optical sensing, industry, aerospace industry, and biomedicine.
A PM fiber achieves high birefringence difference between two polarization modes by stress or deformation. A PM fiber can suppress phase and polarization fluctuations in laser light which may be caused by stress, deformation, temperature or composition and shape defects in the fiber. However, the polarization state of the laser light in the fiber will be changed if the external interferences are strong. Another challenge in implementation of a PM fiber laser is that it can be very difficult to align the stress axis of a PM fiber to be parallel to the polarization direction of the input laser. If the fiber stress axis and the polarization direction of the input laser are not strictly parallel, the two polarization modes in the fiber interfere with each other when external disturbances increase, which can cause polarization extinction ratio to decline and optical noise to increase, and can seriously affect laser output stability.
There is therefore a need for a fiber laser device that has high extinction coefficient and insensitive to external interferences.